The broad goal of this research is to describe the structural and thermodynamic features of the interaction of hydropbobic molecules with alkyl chains of lipid bilayers using x-ray and neutron diffraction. The specific problem to be studied is the interaction of alkane molecules with oriented lipid multilayers. We wish to understand (1) the distribution with respect to thickness of alkanes dissolved in bilayers, (2) the structural modifications of bilayers induced by the alkanes, (3) the thermodynamics of the alkane-bilayer interaction, and (4) the spatial constraints of packing alkanes into bilayers. In addition, we will examine the hypothesis that the mass density of the bilayer interior is uniform and the same as in bulk alkyl liquids. These problems are fundamental to understanding interactions in biological membranes. Neutron diffraction and x-ray diffraction will be used to make complete determinations of the structure of alkane/bilayer systems on an absolute scale. Direct composition measurements will provide supporting data for the structural work and basic thermodynamic parameters of the alkane/bilayer interaction. Differential scanning calorimetry will provide information on the phase behavior of the system and complementary data for the structural and composition measurements.